Function normalize_step_numbers 

pub fn normalize_step_numbers(sop: &mut Sop)

Renumber steps to a contiguous 1..=N sequence (positional order wins) and remap every internal reference: routing.next, depends_on, switch goto targets, and on_failure: goto. References to steps that no longer exist are dropped (goto falls back to Fail). No-op when step numbers are ambiguous (duplicates), since a remap would guess. Runs automatically inside save_sop.